Avascular necrosis (AVN) of the femoral head

• The most common cause ~ of is Legg-Calvé-Perthes disease, an idiopathic disease that occurs primarily in boys between ages 4 and 8 years.
• non-idiopathic etiologies may include trauma, infection, prolonged steroid treatment, sickle cell disease, mucopolysaccharidoses, and epiphyseal dysplasia
• Pain is usually mild, and a limp may be present for several months before medical attention is sought ("painless limp") - (vs painful limp: SCFE)
• Ipsilateral gluteal weakness (Trendelenburg)
• Loss of medial (internal) rotation and abduction are the primary physical  findings.
• Early x-rays  may be negative, but then get widening of medial joint space or a smaller femoral head; flattening of femoral head, then reossification and healing.
• . MRI or bone scan can be helpful early if x-rays are normal. Epiphyseal dysplasia may also be seen on XR (note that bilateral symmetrical involvement is very rare in LCP disease).
• Stages of LCP that can be seen on XR are
  1. synovitis
  2. necrosis
  3. fragmentation
  4. reconstitution
• Usually self-limited
• Treatment includes rest, NSAIDS, bracing, and possible surgery

CHLA Board Review 2005